I have two Sealed Lead Acid Batteries that say 1.3Ah, 20HR. I'm pretty sure this is the same thing as 1.3 Ah (20 Hour rate). Now, does this mean the battery has a total of 1.3 Ah (which would be pathetic for a large scale robot), or does this mean that the battery has a total of 1.3 x 20 (26 Amp hours?) I want to make sure I understand my batteries.

Okay, so to determine the total amp hours for the best performance of the battery, you divide 20hours (or whatever the time frame might be) into the listed Amp hours.

In my case, 1.3 Amp/20HR= a steady 65 amps in 20 hours, giving off a total 1.3 amps in those 20 hours. Let me do the math here:

If my battery disappates 1.3 Amps in 20 hours, than that means it disappates 26 Amps in one hour. Correct?

So if I have two motors that draw on average 5 amps each, 26/5 = 5.2 hours... then the other motor 5.2/5= 1 2/5 hours. That's pretty fair, I guess, considering that I have two of them. Wired in parallel that gives me 2 4/5 hours. Almost three hours if those batteries are only powering the motors, and that assuming the robot's motors will always be rotating and the robots never stationary. (Hopefully the motors will draw less, say 3 amps [There stall current is 10 Amps]. I have a second power supply for the robot's servos, and a third for its on-board computer.

Wow, that was fun. I think I've learned a thing or two about batteries.

Am I correct?

Modified:

Wait a minute, that's not right. 65mA in 20 Hours, 0.065 * 20 = 1.3...wait a minute, if I use those batteries to power two motors that draw 5 amps each those batteries'll zapped in a heartbeat!

As sdk32285 said (I learn something every day) is that they slowly drain the battery over 20 hours when the manufacturer rates the battery in the lab. So basically 1.3A/20h = 0.065A drain for 20 hours. If they ran the test over 10 hours, that 1.3A rating might end up being 1.4Ah, or 1.2Ah, simply because the drain rates aren't perfectly linear. sdk32285 said 20h is the industry standard, that way all manufacturers rate their batteries in the same fair way.

As sdk32285 said (I learn something every day) is that they slowly drain the battery over 20 hours when the manufacturer rates the battery in the lab. So basically 1.3A/20h = 0.065A drain for 20 hours. If they ran the test over 10 hours, that 1.3A rating might end up being 1.4Ah, or 1.2Ah, simply because the drain rates aren't perfectly linear. sdk32285 said 20h is the industry standard, that way all manufacturers rate their batteries in the same fair way.

If weight is a major concern and money isn't, I'd suggest looking at LiPo such as MaxAmps.com. They are very high capacity and you can wire two in parallel for more capacity, whereas with NiMH and NiCd you can only wire them in series.

I hear that if you wire NiCd and NiMH in parallel, they will auto-self-discharge; that's why nobody in the RC hobby ever wires together two in parallel for increased runtime but instead goes up a cell size or switches to LiPo. Then again, I have never tried it in fear of damaging the expensive Sub-C cells like IB4200 and GP4300, so I'll take your word on this one.

The self discharge happens with any battery type, when you put two batteries together in parallel that do not have equal charges. You must make sure that both batteries are the same exact type, and you should only charge and discharge them while connected in parallel.

You also should not combine an old battery with a new battery, even if they are the same type, as the discharge rates will be different.

Are you sure they have that much power? They say real bold on this sight that they're 3600 mah, but then in small type, listed under "BPK-3200N-12 BattlePacks" that they're 60ah continuous? You did see the link, did you? I just want to make sure, because that sounds like a really good deal!

Sorry if I sound a little incredulous. I just want to know for certain how much power those batteries in the link have...

Heh, reminds me of the time I was soldering leads onto a very high quality IB4200 pack. The solder in wire form touched both terminals at once accidentally (they're about 6 inches apart!) The current flow was too much for the solder and it melted on the other terminal.